Ignition system utilizing a rotatable commutator in combination with a saturable capacitor



July 5, 1966 0. K. NILSSEN 3, 5

IGNITION SYSTEM UTILIZING A HOTATABLE COMMUTATOR IN COMBINATION WITH A SATURABLE CAPACITOR Filed Jan. 2, 1964 2 Sheets-Sheet 1 Q INVENTOR. Q IV/LS'SE/V W BY gala a M y ATTOIP/VEYS July 5, 1966 0. K. NILSSEN 3 5 IGNITION SYSTEM UTILIZING A ROTATABLE COMMUTATOR IN COMBINATION WITH A SATURABLE CAPACITOR Filed Jan. 2, 1964 2 Sheets-Sheet 2 S RN Y m 5 NS N wsf N mu gmm J N z r M= Mm K m 23: 5 M4, w a K 9W am m I Q 9 H0 OW F s United States Patent 3 259 799 IGNITION SYSTEM imirzING A ROTATABLE COMMUTATOR 1N COMBINATION WITH A SAT- URABLE CAPACITOR Ole K. Nilssen, Livonia, Mich., assignor to The Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,037 4 Claims. (Cl. 315-214) This invention relates to an ignition system for an internal combustion engine and more particularly to such an ignition system in which a rotatable com-mutator in combination with a saturable capacitor is employed to switch the current in the primary circuit of the ignition system.

In present day conventional ignition systems for internal combustion engines, ignition contact breaker points are employed for interrupting the current in the primary circuit of the ignition system. As a result, a high voltage is induced in the secondary winding of the ignition coil and this voltage or energy is applied to the spark plugs through the distributor to fire the combustible mixtures in the engine cylinders. The reason for the use of the contact breaker points in preference to other switching mechanisms is that it opens the .primary circuit rapidly and if suitable means are employed, interrupts the current sufiiciently rapidly to produce the ignition voltages in the secondary winding necessary to fire the spark plugs.

Although the ignition contact breaker points currently used are satisfactory from a performance standpoint, by furnishing suflicient voltages in the secondary winding of the ignition coil to fire the spark plugs, they leave something to be desired with regard to durability and reliability. It is well known that ignition contact breaker points must be replaced in the range of 15,000 to 20,000 miles to produce optimum performance in a passenger car internal combustion engine. This deterioration in the ignition contact breaker points is brought about by arcing as the contact breaker points open and close.

The present invention is designed to provide a highly satisfactory ignition system both from the performance and durability standpoints. In this system, a rotatable cylindrical commutator is employed to switch or interrupt the current flowing in the primary winding of the ignition coil. While a commutator for this purpose has been proposed in the past, the performance of a system using it has not been entirely satisfactory. This has been due to the fact that the necessary high voltage in the secondary winding of the ignition coil have not been produced because of slow switching times and arcing at the commutator brushes as the brushes move from a conductive to a nonconductive region on the commutator. The arcing also shortens the life of the commutator and brushes to unsatisfactory levels.

In the present invention, a saturable capacitor is positioned across the commutator. As the com-mutator commences to interrupt the current flowing in the primary circuit, the current will shift to the saturable capacitor. The charge acceptance capacity of the saturable capacitor should be large enough so that the commutator moves one of its conducting regions out of engagement with a switching brush on the commutator and moves one of its non-conductive regions into engagement with the switching brush prior to the time that the saturable capacitor is saturated. This will prevent a large voltage rise across the commutator until the brush of the commutator is in the nonconductive region and will permit a high. rise in ignition voltage when the saturable capacitor becomes saturated. The saturable capacitor will,

therefore, delay the voltage rise across the commutator until the switching brush of the commutator comes out of engagement with a conductive region of the commutator. This prevents arcing from occurring as the brush effectively moves from a conducting to a nonconducting region of the commutator.

An object of the present invention is the provisionof an ignition system for an internal combustion engine.

that will produce the required ignition voltages and that will be durable and have a very long life.

A further object of the invention is the provision of an ignition system for an internal combustion engine in which the durability and reliability of the system is improved over the conventional internal combustion engine ignition system.

A further object of the invention is the provision of an ignition system for an internal combustion engine in which means are provided for switching the primary current of the. ignition system that has a very long satise factory operating life when compared with the switch-. ing mechanisms used in conventional internal combustion systems.

Other objects and attendant advantages of the present invention will become more fullyapparent as the specification is considered in connection with the attached drawings in which:

FIGURE 1 is a circuit diagram of one embodiment of the invention;

FIGURE 2 is a layout view of the commutator of the present invention;

FIGURE 3 is a circuit diagram of another embodiment of the present invention;

FIGURE 4 is a hysteresis loop of a saturable capacitor employed with the embodiment of the invention shown by the circuit diagram of FIGURE 1, and

FIGURE 5 is an idealized hysteresis loop of a satura- -ble capacitor used with the circuit diagram of FIG- URE 3.

Referring now to the drawings in which like reference numerals designate like parts throughout the several views thereof, there is shown in FIGURE 1 an ignition system for an internal combustion engine that includes a source of electrical energy, for example, a storage-battery 10, having one electrode 11 connected to ground through a lead 12. The other electrode 13 of the bat? tery 10 is connected to one terminal of the primary winding 14 of ignition coil 15 through an ignition switch 16 and a resistor 17. The other terminal of the primary winding 14 is connected to a junction 18 by means of a lead 19.

A rotatable commutator 21 is provided for interrupting current flow in the primary winding 14. Thiscommutator includes a commutator shaft 22 that may be mounted for rotation in a distributor 23 0f an internal combustion engine. The distributor is designated schematically, but it is to be understood that it may be'any conventional internal combustion engine distributor with the commutator shaft 22 connected to the shaft of the distributor driven by the internal combustion engine. The commutator 21 has a cylindrical body 24 constructed of an insulating material, for example, Bakelite or plastic, mounted on and supported by the shaft 22. Positioned over the cylindrical surface of the cylindrical body 24 is a cylindrical conducting sheath 25 that has alternate segments cut away as shown at 26.. It can be seen that the cut. away segments 26 expose the nonconducting material2'4 but do not extend through theaxial length of the cylindrical body 24; This leaves a continuous cylindrical band 27 of conducting material for a. small portion of the axiallength of the cylindrical'body 24 Patented July 5, 1966 and alternate conducting segments 30 and nonconducting Segments 26 over the remainder of the axial length of the commutator.

An electrical contact brush 31 is connected to the junction 18 through a lead 32, and this brush has a width not greater than and preferably substantially equal to the width of the nonconducting segments 26 and conducting segments 30 of the commutator 21,.as shownin FIGURE 2. A second brush 33 is positioned in engagement with the continuous cylindrical band 27 of conducting material, and it should have a width substantially equal to, but not greater than the width of this continuous cylindrical band. The brush 33 is connected to ground through leads 35 and 36.

A saturable capacitor 37 is connected across the cornmutator 21 by connecting one terminal to brush 31, through junction 18 and lead 32, and the other terminal to brush 33 by means of the lead 38. As will be explained more fully subsequently, this saturable capacitor should have a hysteresis loop as shown in FIGURE 4.

The ignition coil 15 includes a secondary winding 41 having one terminal connected to ground through a lead 42 and the other terminal connected to a rotatable arm 43 of distributor 23 through a lead 44. The rotatable arm 43 is adapted to sequentially come into electrical engagement with space. contacts 45 through 50 of distributor 23 that are connected to spark plugs 51 through 56 by means of leads or spark plug wires 57 through 62. It is to be understod, as shown by the dashed lines, that rotatable arm 43 is rotatable in synchronism with the commutator 21 so that one of the conducting portions 30 of the commutator 21 is moved out of engagement with brush 31 and one of the nonconducting segments 26 is rotated into engagement with brush 31 when the rotatable arm 43 is coming into engagement with one of the contacts 45 through 50.

In the operation of the ignition system shown in FIG- URE 1, current will flow in the primary winding 14 of ignition coil 15, assuming that ignition switch 16 is closed, when the brush 31 is in engagement with a conducting segment 30 of the electrical conducting sheath 25. In this position, the electrical conducting sheath 25 of commutator 21 affords a substantial short circuit between the junction 18 and ground since the brushes 31 and 33 are essentially short circuited through the conducting segment 30 and the continuous cylindrical conducting band 27 of the sheath 25. This permits a large current to flow in the primary winding 14 of the ignition coil 15. At this time also it can be appreciated that there is no voltage drop or potential difference across the terminals of the saturable capacitor 37 since the brushes 31 and 33 are at the same potential. The saturable capacitor 37 will be in a position, shown by the letter A on the hysteresis loop of FIGURE 4, with a certain amount of residual or remanent charge, if it has previously been charged. At this time, the rotatable arm 43 will be in position between two of the contacts 45 through 50 as shown in FIG- URE 1.

When the commutator 21 rotates into a position where a conducting segement 30 rotates out of engagement with brush 31 and a nonconducting segment 26 rotates into engagement with brush 31, the rotatable arm 43 will be coming into engagement with one of the contacts 45 through 50. At this time the voltage across the primary winding 14 of the ignition coil 15 and across the commutator 21 attempts to rise, since the current through the primary winding 14 is being interrupted and by operation of Lenzs law a large voltage is induced in the primary winding 14 to maintain the current flow constant in this circuit. As a result of the increased resistance at the commutators 21, this voltage rise is many times greater than the initial voltage drop across the primary winding 14 and is many times greater than the terminal voltage of the battery 10,

The saturable capacitor 37 essentially delays this voltage rise by accepting the charge represented by the current flow and providing an alternate current path for this current. As shown in FIGURE 4, the slope from the point A where zero volts are impressed across the capacitor 37 to the knee of the curve at point B is quite steep and provides a delay determined by the charge acceptance capacity of the saturable capacitor 37 in coulombs or amp-secs between points A and B. Thus the voltage will not rise substantially across the capacitor 37 and hence across the brushes 31 and 33 of commutator 21 until the voltage has reached the knee of the curve at point B. For the application shown here, a saturable capacitor in which the voltage at the knee of the curve point B is 3 or 4 volts would be entirely satisfactory. At this time, the saturable capacitor will go into saturation and the voltage across the saturable capacitor 37 and the commutator 21 will rise from the point B along the line C which has a slope much less than the curve between the points A and B. At this time, then the voltage across the commutator 21 and the primary winding 14 is free to rise to provide the high ignition voltages in the secondary winding 41 that are necessary to fire the spark plugs.

It can be appreciated that the voltage rise across the commutator 21 and the primary winding 14 is delayed by an amount determined by the time necessary to charge the capacitor from the point A to point B on the curve shown 'in FIGURE 4. While a small voltage rise is permitted during this time, it is insufficient to cause deteriorating arcing to occur as the brush 31 moves from a conducting segment 30 to a nonconducting segment 26 of the commutator. For example, if'it takes a charge of 10 coulombs to move from point A to point B on the curve shown in FIGURE 4 and 10 amperes of current is flowing in the primary winding 14 initially, then the delay in the large voltage rise across the saturable capacitor 37'and the commutator 21 on the curve, or the time necessary to move from point A to point B will be microseconds. This delay will permit the brush 31 to move effectively out of engagement with a conducting segment 30 and into engagement with the nonconducting segment 26 prior to the large voltage rise along the line C of the curve. As a result, destructive arcing will not occur and proper ignition voltages will be produced. In order to accomplish this, the brush 31 should have a small thickness, for example, the brush 31' should occupy one degree out of the 360 degrees around the periphery of the commutator 21. For the purposes of clarity, the thickness of the brush 31 has been exaggerated in FIGURE 2.

FIGURE 3 shows an alternate form of the invention in which a saturable capacitor 37 made of a square loop material having the idealized hysteresis loop shown in FIGURE 5 may be employed. This saturable capacitor 37 should be made of a material in which the ratio of saturation charge to residual or remnant charge is quite small, for example, on the order of 1.1 or 1.2.

In the circuit shown in FIGURE 3, the saturable capacitor 37 is biased into one of its saturated states by a voltage substantially equal to the coercive voltage of the capacitor 37. This is accomplished by placing an ordinary linear capacitor 71 in series with the saturable capacitor 37. This capacitor 71 has one terminal connected to a junction 72 and the other terminal connected to the brush 33. The junction 72 is connected to a junction 73 of a voltage divider 74, comprised of resistors 75 and 76, by means of a lead 77. It can be appreciated that the voltage divider 74 divides the voltage of the battery 10 and applies a portion of it, for example, 3 or 4 volts to .the junction point 72 and that the-capacitor 71 charges to this voltage.

When commutator 21 is in a position where the brushes 31 and 33 are short circuited through the electrical conductive sheath 25, that is, when the brush 31 is in contact with one of the conductive segments 30, the junction point 18 and thus one terminal of the capacitor will be essentially at ground potential since the junction point 18 is connected to ground through the lead 32, brush 31, the conductive sheath 25 of commutator 21, brush 33, lead 35 and lead 36. The other terminal of the saturable capacitor 37 that is connected to the junction 72 Will have a positive potential determined by the voltage divider 74 of approximately 3 or 4 volts. If the coercive voltage of the saturable capacitor 37 is substantially equal to this potential, and such capacitors are readily available, then the saturable capacitor 37 will be in the position on the hysteresis loop shown by the letter D in FIGURE 5. In other words, it will be biased in the positive direction and charged close to saturation.

When the commutator 21 is rotated so that one of the conducting segments 30 moves out of engagement with the brush 31 and a nonconducting segment 26 moves into engagement with the brush 31, the voltage of the primary winding 14 attempts to rise very rapidly to maintain steady current flow under the increased resistance produced by the commutating action. This will cause the voltage across the capacitor 37 to reverse polarity so that the terminal connected to the junction 18 is much more positive than the terminal connected to the junction 72. As a result, the voltage across the capacitor 37 will new become negative in terms of the hysteresis loop shown in FIGURE 5 rather than positive and the capacitor will be switched from point D to the point E on the hysteresis loop or" FIGURE 5. During the time that it is switching, however, the voltage rise across the saturable capacitor 37 and hence across the brushes 31 and 33 is limited to twice the coercive voltage of the saturable capacitor, or in the neighborhood of 6 to 8 volts.

After a time delay determined by the saturation charge in coulombs or amp-sec. of the saturable capacitor 37 in moving from point D to point E on the hysteresis loop of FIGURE 5, the voltage is free to rise across the saturable capacitor 37 and the commutator 21 and hence in the primary winding 14 of the ignition coil 17 along the line F. This produces the high voltages in the secondary winding 41 necessary for proper ignition of the combustible mixtures in the cylinders of the internal combustion engine. If the saturation charge of the saturable capacitor 37 is 10 coulombs, and .if 10 amperes of current were initially flowing in the primary winding 14 of ignition coil 15, a delay of 200 microseconds will be encountered before the voltage across the saturable capacitor 37 and the brushes 31 and 33 rises above twice the coercive voltage (6 to 8 volts), the distance along the abscissa from point D to point E in FIGURE 5. This delay should be adequate to permit a conducting segment 3%) to move totally out of engagement with brush 31. This prevents any destructive arcing that may otherwise occur. After this delay, the voltage across the commutator 21 and the primary winding 14 is free to rise along line F to a level to induce satisfactory ignition voltages in secondary winding 41 of ignition coil 15.

In the embodiment shown in FIGURE 1 the capacitor 37 may be a disc ceramic capacitor made of a Ceramite material. For example, a Sprague series SI-IK type P10 saturable capacitor would have a hysteresis loop similar to that shown in FIGURE 4 and would permit proper operation of the circuit shown in FIGURE 1. In the embodiment shown in FIGURE 5, a barium titanite saturable capacitor should be used. This saturable capacitor should be made of the crystalline form of BaTiO and it will have an essentially square hysteresis loop as represented by the idealized hysteresis loop shown in FIGURE 5.

The present invention thus provides an efiective, reliable and long lasting ignition system for an internal combustion engine. It requires very little maintenance and should not require the periodic replacement of the switching element of the ignition system as is now required in present day internal combustion ignition systems.

It is to be understood that this invention is not to be limited to the eXact construction shown and described,

but that various changes and modifications-may be niade without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An ignition system for an internal combustion 'engine comprising, a spark plug, an ignition coil having a primary and a secondary winding, means electrically coupling said spark plug and said secondary winding, a source of electrical energy, a commutator including terminals connected in circuit with said source of electrical energy and said primary winding of said ignition coil, said commutator being rotatable by means coupled to said internal combustion engine, said commutator including means for periodically interrupting current through said primary winding of said ignition coil, first means including a saturable capacitor connected to said primary winding of said ignition coil and across the terminals of said commutator, said saturable capacitor constructed of a material having a substantially square hysteresis loop and having a small saturation charge to remnant charge ratio, said first means including means coupled to said source of electrical energy and said saturable capacitor for applying a voltage to said saturable capacitor at least equal to the coercive voltage of said saturable capacitor and of a polarity opposite to the polarity of the voltage applied across said saturable capacitor as said commutator interrupts current in said primary winding.

2. The combination of claim 1 in which said last mentioned means comprises a voltage divider connected across said source of electrical energy and a linear capacitor connected in series with said saturable capacitor across said commutator with means coupling said voltage divider and said linear capacitor to charge said linear capacitor to the fraction of the voltage of said source of electrical energy as determined by said voltage divider.

3. An ignition system for an internal combustion engine comprising, a plurality of spark plugs, an ignition coil having a primary and a secondary winding, a distributor including means operable by the internal combustion engine and coupled to said secondary winding and said spark plugs for sequentially connecting said spark plugs to said secondary coil, a source of electrical energy, a cylindrical commutator operable in synchronism with said first mentioned means, said commutator including a continuous cylindrical band of conductive material, a first electrical contact brush in engagement with said continuous cylindrical band of conductive material, said commutator also including a band of alternate portions of conducting and nonconducting segments with said conducting segments being in electrical contact with said cylindrical band of conducting material, a second electrical contact brush in engagement with said band of alternate portions of conducting and nonconducting segments, one of said brushes connected to said primary winding and the other of said brushes connected to said source of electrical energy, whereby said primary winding of said ignition coil is energized and de-energized when said commutator is rotated in synchronism with said first mentioned means, a saturable capacitor connected across said electrical contact brushes to prevent arcing from occurring as a conducting segment of said commutator moves out of engagement with said second electrical contact brush, said saturable capacitor being constructed of a material having a substantially square hysteresis loop and a relative small saturation charge to remnant'charge ratio and means coupled to said source of electrical energy and said saturable capacitor for applying a voltage to said saturable capacitor at least equal to the coercive voltage of said saturable capacitor and of a polarity opposite to the polarity of the voltage applied to said saturable capacitor when said primary winding of said ignition coil is de-energized.

4. An ignition system for an internal combustion engine comprising, a spark plug, an ignition coil having a primary and a secondary winding, means coupling said spark plug and said secondary winding, a source of electrical energy, a commutator connected in circuit with said source of electrical energy in the primary winding of said ignition coil and rotatable by means coupled to the internal combustion engine, said commutator including means for periodically interrupting current through said primary winding of said ignition coil, a saturable capacitor connected across said commutator, and separate biasing means coupled to said source of electrical energy and said saturable capacitor for applying a voltage to said saturable capacitor sufficient to saturate said saturable capacitor in one direction, said voltage being of a polarity opposite to the polarity of the voltage applied across said saturable capacitor as said commutator interrupts current in said primary Winding.

References Cited by the Examiner UNITED STATES PATENTS 5/1961 Krone 123-146.5

10/1951 Curtis 317-1l OTHER REFERENCES Anderson, J. R; Ferroelectric Storage Elements for Digital Computers and Switching Systems, article in Elec- 10 trical Engineering, October 1952, pp. 916-922. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, A SPARK PLUG, AN IGNITION COIL HAVING A PRIMARY AND A SECONDARY WINDING, MEANS ELECTRICALLY COUPLING SAID SPARK PLUG AND SAID SECONDARY WINDING, A SOURCE OF ELECTRICAL ENERGY, A COMMUTATOR INCLUDING TERMINALS CONNECTED IN CIRCUIT WITH SAID SOURCE OF ELECTRICAL ENERGY AND SAID PRIMARY WINDING OF SAID IGNITION COIL, SAID COMMUTATOR BEING ROTATABLE BY MEANS COUPLED TO SAID INTERNAL COMBUSTION ENGINE, SAID COMMUTATOR INCLUDING MEANS FOR PERIODICALLY INTERRUPTING CURRENT THROUGH SAID PRIMARY WINDING OF SAID IGNITION COIL, FIRST MEANS INCLUDING A SATURABLE CAPACITOR CONNECTED TO SAID PRIMARY WINDING OF SAID IGNITION COIL AND ACROSS THE TERMINALS OF SAID COMMUTATOR, SAID SATURABLE CAPACITOR CONSTRUCTED OF A MATERIAL HAVING A SUBSTANTIALLY SQUARE HYSTERESIS LOOP AND HAVING A SMALL SATURATION CHARGE TO REMNANT CHARGE RATIO, SAID FIRST MEANS INCLUDING MEANS COUPLED TO SAID SOURCE OF ELECTRICAL ENERGY AND SAID SATURABLE CAPACITOR FOR APPLYING A VOLTAGE TO SAID SATURABLE CAPACITOR AT LEAST EQUAL TO THE COERCIVE VOLTAGE OF SAID SATURABLE CAPACITOR AND OF A POLARITY OPPOSITE TO THE POLARITY OF THE VOLTAGE APPLIED ACROSS SAID SATURABLE CAPACITOR AS SAID COMMUTATOR INTERRUPTS CURRENT IN SAID PRIMARY WINDING. 